Here is a list of all documented namespaces with brief descriptions:

[detail level 1234]

▼Nnrfcxx	Primary namespace for nrfcxx functionality
Nboard	Namespace holding board-specific configuration data
Nclock	Functions and classes related to clocks and time
Ncrc	Namespace providing pre-defined checksum algorithms
Ngpio	Abstractions and constants around GPIO capability
Nled	Abstractions and constants around LED capability
Nlpm	Infrastructure to support low-power-mode operations
Nmisc	Namespace for abstractions that aren't handled in another namespace
▼Nnrf5	Namespace holding support for bare nRF5 peripheral instances
Nseries	Namespace holding series-specific implementations that support the genericized API of nrfcxx
Nperiph	Abstractions of nRF51 peripherals
▼Nsensor	Namespace for abstractions of various sensors
▼Nadc	Specializations of nrfcxx::periph::ADC for common ADC operations
NsteinhartHart	Steinhart-Hart configurations for common thermistors and applications
Nutility	Various utilities, probably not dependent on nRF51 at all